I. Field
The present invention relates to data communication. More particularly, the present invention relates to a novel, flexible, and efficient coding scheme for encoding data for transmission on multiple transmission channels with different transmission capabilities.
II. Description of the Related Art
Wireless communication systems are widely deployed to provide various types of communication such as voice, data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), orthogonal frequency division modulation (OFDM), or some other modulation techniques. OFDM systems may provide high performance for some channel environments.
In an OFDM system, the operating frequency band is effectively partitioned into a number of “frequency subchannels”, or frequency bins. Each subchannel is associated with a respective subcarrier upon which data is modulated, and may be viewed as an independent “transmission channel”. Typically, the data to be transmitted (i.e., the information bits) is encoded with a particular coding scheme to generate coded bits. For a high-order modulation scheme (e.g., QPSK, QAM, and so on), the coded bits are grouped into non-binary symbols that are then used to modulate the subcarriers.
The frequency subchannels of an OFDM system may experience different link conditions (e.g., different fading and multipath effects) and may achieve different signal-to-noise-plus-interference ratio (SNR). Consequently, the number of information bits per modulation symbol (i.e., the information bit rate) that may be transmitted on each subchannel for a particular level of performance may be different from subchannel to subchannel. Moreover, the link conditions typically vary with time. As a result, the supported bit rates for the subchannels also vary with time.
The different transmission capabilities of the frequency subchannels plus the time-variant nature of the capabilities make it challenging to provide an effective coding scheme capable of encoding the supported number of information bits/modulation symbol to provide the required coded bits for the subchannels
Accordingly, a high performance, efficient, and flexible coding scheme that may be used to encode data for transmission on multiple subchannels with different transmission capabilities is highly desirable.